The invention involves a hydraulic impact device that has a cylinder which holds the end of the tubing and contains the turning gear for the tubing, and which contains a percussion piston that acts upon the tubing and can move back and forth inside an inner boring; the percussion piston is controlled via a control system that contains rotary valves driven by a rotary engine.
One hydraulic impact device of this type is known-in-the-art from DE-OS 22 014.6. In this impact device, the component that is necessary for the gear reversal is the rotary valve that surrounds the actual percussion piston. In addition to a costly control system, it is a significant disadvantage of this device that its structure requires it to be of sizeable dimensions. It is an additional disadvantage that, with the control system that is used, the power output changes with changes in the impact rate and impact force, so that the control system as a whole is relatively imprecise. The same is true for the device specified in DE-OS 43 28 278.4, in which again the rotary valve is arranged around the percussion piston. In this device the rotary valve is driven via a rotary engine, which simultaneously serves in the displacement of the tubing, in which a shifting of the interlocking gearwheels also enables a separation of the rotary valve mechanism from the turning gear of the tubing. Thus this device contains both mechanical connections and toothed wheel works, which in turn also results in increased manufacturing costs as well as a certain variation of impact rate, impact force, and impact power output. More importantly, however, it is not possible to produce extension borings or to use the device with different hammers having different values, because the device, which has been manufactured as a complete unit, must be operated as such.